Factors influencing acute loss of lung compliance and alveolar stability remain obscure. This project undertakes the study of one model of stiffening, as produced by hyperventilation of excised lungs. This model also serves as a tool to examine the role of changes in elastic recoil in determining the maximum expiratory flow. Comparative studies of lung mechanical properties of rodents and carnivores are underway. Small mammals with short life spans such as the mouse may offer some experimental advantages in the study of age-related pulmonary changes. Neural influences on lung surfactant and on fluid transudation into interstitial or alveolar spaces are presently poorly understood. The mechanism of effect of both sympathetic stimulation and CNS lesions on lung function are under investigation.